Image Processing Device, Image Processing Method, Microscope System, and Computer-Readable Recording Medium

1. An image processing device comprising: a processor comprising hardware, wherein the processor is configured to: acquire a plurality of images of different imaging fields of view on the same subject; select, from the plurality of images acquired, in which a common region of a predetermined size is set at a common position in the individual images, a plurality of image pairs that are combinations of images in which a subject image in the common region in one image corresponds to a subject image in a region other than the common region in another image; calculate a correction gain for performing shading correction, based on a pixel value of a pixel contained in the common region and a pixel value of a pixel contained in a region corresponding to the common region, for each combination of the one image and the another image; and correct shading produced in a correction-target image, using the correction gain calculated, wherein the common region is a central region when each image included in the plurality of images is divided by the same odd number not less than three in each of a first direction and a second direction orthogonal to the first direction, and wherein when the number of divisions in each of the first and second directions is N, the length of the imaging field of view in the first direction is L A , and the length of the imaging field of view in the second direction is L B , the processor is configured to acquire the plurality of images by: controlling an image sensor to perform imaging {(N−1)/2+1} times while controlling an actuator to move the imaging field of view by the length of L A /N at a time in the first direction; controlling the image sensor to perform imaging (N−1)/2 times while controlling the actuator to move the imaging field of view by the length of L B /N at a time in the second direction from one end of an imaged region; and further controlling the image sensor to perform imaging (N−1)/2 times while controlling the actuator to move the imaging field of view by the length of L A /N at a time in the first direction from another end of an imaged region.

2. The image processing device according to claim 1 , wherein the processor is configured to: control a storage to sequentially store the correction gain calculated; and calculate a composite correction gain using a plurality of correction gains calculated on the same region in the image.

3. A microscope system comprising: the image processing device according to claim 1 ; a light source configured to illuminate the subject; the image sensor; the actuator; and an optical system configured to guide transmitted light or reflected light from the subject to the image sensor.

4. The image processing device according to claim 1 , wherein the number of divisions in each of the first and second directions is set based on a region in each of the images where a brightness attenuation rate relative to the center of the image is less than or equal to a predetermined value.

5. The image processing device according to claim 1 , wherein when the number of divisions in each of the first and second directions is N, the processor is configured to: control the image sensor to acquire at least (3N−1)/2 images; and select at least (N 2 − 1)/2 image pairs.

6. An image processing device comprising: a processor comprising hardware, wherein the processor is configured to: acquire a plurality of images of different imaging fields of view on the same subject; select, from the plurality of images acquired, in which a common region of a predetermined size is set at a common position in the individual images, a plurality of image pairs that are combinations of images in which a subject image in the common region in one image corresponds to a subject image in a region other than the common region in another image; calculate a correction gain for performing shading correction, based on a pixel value of a pixel contained in the common region and a pixel value of a pixel contained in a region corresponding to the common region, for each combination of the one image and the another image; and correct shading produced in a correction-target image, using the correction gain calculated, wherein the common region is a central region when each image included in the plurality of images is divided by the same odd number not less than three in each of a first direction and a second direction orthogonal to the first direction, and wherein when the number of divisions in each of the first and second directions is N, the length of a side of the imaging field of view in the first direction is L A , and the length of a side of the imaging field of view in the second direction is L B , the processor is configured to acquire the plurality of images acquired by: controlling an image sensor to perform imaging N times while controlling an actuator to move the imaging field of view by a length of L A /N at a time in the first direction; and with an imaging position at the (N+1)/2nd time in the first direction as a starting point, controlling the image sensor to perform imaging (N−1)/2 times while controlling the actuator to move the imaging field of view by the length of L B /N at a time in the second direction.

7. The image processing device according to claim 6 , wherein the number of divisions in each of the first and second directions is set based on a region in each of the images where a brightness attenuation rate relative to the center of the image is less than or equal to a predetermined value.

8. The image processing device according to claim 6 , wherein when the number of divisions in each of the first and second directions is N, the processor is configured to: control the image sensor to acquire at least (3N−1)/2 images; and select at least (N 2 −1)/2 image pairs.

9. The image processing device according to claim 6 , wherein the processor is configured to: control a storage to sequentially store the correction gain calculated; and calculate a composite correction gain using a plurality of correction gains calculated on the same region in the image.

10. A microscope system comprising: the image processing device according to claim 6 ; a light source configured to illuminate the subject; the image sensor; the actuator; and an optical system configured to guide transmitted light or reflected light from the subject to the image sensor.

11. An image processing method comprising: acquiring a plurality of images of different imaging fields of view on the same subject; selecting, from the plurality of images acquired, in which a common region of a predetermined size is set at a common position in the individual images, a plurality of image pairs that are combinations of images in which a subject image in the common region in one image corresponds to a subject image in a region other than the common region in another image; calculating a correction gain for performing shading correction, based on a pixel value of a pixel contained in the common region and a pixel value of a pixel contained in a region corresponding to the common region, for each combination of the one image and the another image; and correcting shading produced in a correction-target image, using the correction gain calculated, wherein the common region is a central region when each image included in the plurality of images is divided by the same odd number not less than three in each of a first direction and a second direction orthogonal to the first direction, and wherein when the number of divisions in each of the first and second directions is N, the length of the imaging field of view in the first direction is L A , and the length of the imaging field of view in the second direction is L B , acquiring the plurality of images comprises: controlling an image sensor to perform imaging {(N−1)/2 +1} times while controlling an actuator to move the imaging field of view by the length of L A /N at a time in the first direction; controlling the image sensor to perform imaging (N−1)/2 times while controlling the actuator to move the imaging field of view by the length of L B /N at a time in the second direction from one end of an imaged region; and further controlling the image sensor to perform imaging (N−)/2 times while controlling the actuator to move the imaging field of view by the length of L A /N at a time in the first direction from another end of an imaged region.

12. A non-transitory computer-readable recording medium recording an image processing program for causing a computer to at least: acquire a plurality of images of different imaging fields of view on the same subject; select, from the plurality of images acquired, in which a common region of a predetermined size is set at a common position in the individual images, a plurality of image pairs that are combinations of images in which a subject image in the common region in one image corresponds to a subject image in a region other than the common region in another image; calculate a correction gain for performing shading correction, based on a pixel value of a pixel contained in the common region and a pixel value of a pixel contained in a region corresponding to the common region, for each combination of the one image and the another image; and correct shading produced in a correction-target image, using the correction gain calculated, wherein the common region is a central region when each image included in the plurality of images is divided by the same odd number not less than three in each of a first direction and a second direction orthogonal to the first direction, and wherein when the number of divisions in each of the first and second directions is N, the length of the imaging field of view in the first direction is L A , and the length of the imaging field of view in the second direction is L B , the plurality of images are acquired by the image processing program causing the computer to at least: control an image sensor to perform imaging {(N−1)/2+1} times while controlling an actuator to move the imaging field of view by the length of L A /N at a time in the first direction; control the image sensor to perform imaging (N−1)/2 times while controlling the actuator to move the imaging field of view by the length of L B /N at a time in the second direction from one end of an imaged region; and further control the image sensor to perform imaging (N−1)/2 times while controlling the actuator to move the imaging field of view by the length of L A /N at a time in the first direction from another end of an imaged region.

13. An image processing method comprising: acquiring a plurality of images of different imaging fields of view on the same subject; selecting, from the plurality of images acquired, in which a common region of a predetermined size is set at a common position in the individual images, a plurality of image pairs that are combinations of images in which a subject image in the common region in one image corresponds to a subject image in a region other than the common region in another image; calculating a correction gain for performing shading correction, based on a pixel value of a pixel contained in the common region and a pixel value of a pixel contained in a region corresponding to the common region, for each combination of the one image and the another image; and correcting shading produced in a correction-target image, using the correction gain calculated, wherein the common region is a central region when each image included in the plurality of images is divided by the same odd number not less than three in each of a first direction and a second direction orthogonal to the first direction, and wherein when the number of divisions in each of the first and second directions is N, the length of a side of the imaging field of view in the first direction is L A , and the length of a side of the imaging field of view in the second direction is L B , acquiring the plurality of images comprises: controlling an image sensor to perform imaging N times while controlling an actuator to move the imaging field of view by a length of L A /N at a time in the first direction; and with an imaging position at the (N+1)/2nd time in the first direction as a starting point, controlling the image sensor to perform imaging (N−1)/2 times while controlling the actuator to move the imaging field of view by the length of L B /N at a time in the second direction.

14. A non-transitory computer-readable recording medium recording an image processing program for causing a computer to at least: acquire a plurality of images of different imaging fields of view on the same subject; select, from the plurality of images acquired, in which a common region of a predetermined size is set at a common position in the individual images, a plurality of image pairs that are combinations of images in which a subject image in the common region in one image corresponds to a subject image in a region other than the common region in another image; calculate a correction gain for performing shading correction, based on a pixel value of a pixel contained in the common region and a pixel value of a pixel contained in a region corresponding to the common region, for each combination of the one image and the another image; and correct shading produced in a correction-target image, using the correction gain calculated, wherein the common region is a central region when each image included in the plurality of images is divided by the same odd number not less than three in each of a first direction and a second direction orthogonal to the first direction, and wherein when the number of divisions in each of the first and second directions is N, the length of a side of the imaging field of view in the first direction is L A , and the length of a side of the imaging field of view in the second direction is L B , the plurality of images are acquired by the image processing program causing the computer to at least: control an image sensor to perform imaging N times while controlling an actuator to move the imaging field of view by a length of L A /N at a time in the first direction; and with an imaging position at the (N+1)/2nd time in the first direction as a starting point, control the image sensor to perform imaging (N−1)/2 times while controlling the actuator to move the imaging field of view by the length of L B /N at a time in the second direction.